Turbochargers for gasoline and diesel internal combustion engines are known devices used in the art for pressurizing or boosting the intake air stream, routed to a combustion chamber of the engine, by using the heat and volumetric flow of exhaust gas exiting the engine. Specifically, the exhaust gas exiting the engine is routed into a turbine housing of a turbocharger in a manner that causes an exhaust gas-driven turbine to spin within the housing. The exhaust gas-driven turbine is mounted onto one end of a shaft that is common to a radial air compressor mounted onto an opposite end of the shaft. Thus, rotary action of the turbine also causes the air compressor to spin within a compressor housing of the turbocharger that is separate from the exhaust housing. The spinning action of the air compressor causes intake air to enter the compressor housing and be pressurized or boosted a desired amount before it is mixed with fuel and combusted within the engine combustion chamber.
The amount by which the intake air is boosted or pressurized is controlled by regulating the amount of exhaust gas that is passed through the turbine housing by an exhaust bypass system or wastegate. The wastegate is actuated, during turbocharger operation when the boost pressure is approaching a maximum desired pressure, to divert an amount of exhaust gas away from the turbocharger turbine housing to reduce the rotational speed of the turbine and, thereby reduce the rotational speed of the air compressor and reduce the amount by which the intake air is pressurized. EGR is a known method for reducing NOX emissions in internal combustion engines. For effective use, an EGR system must overcome the adverse pressure gradient created by a positive pressure gradient across the engine, which is typical for example of modem high-efficiency diesel engines in at least a portion of their operating range. A conventional EGR system comprises a control valve that regulates the amount of exhaust gas that is taken from an engine exhaust manifold and returned to an engine induction system for mixing with the intake air and subsequent combustion. The EGR control valve is an ancillary device that is separate from both the engine and turbocharger. The conventional EGR system also includes a pump, separate from the turbocharger and engine, that increases the pressure of the returned exhaust gas routed by the EGR control valve to the induction system, to match the intake air charge or boost pressure exiting the turbocharger, thereby overcoming the positive pressure gradient across the engine.
Modem engine compartments, especially those of turbocharged internal combustion engines, are configured having minimal space for devices ancillary to the engine itself, thereby making use of such conventional EGR systems, comprising a separate control valve, pump, and exhaust and intake manifold bypasses, and related manifolding and plumbing difficult and sometimes impossible. It is, therefore, desirable that one or more devices of an EGR system be constructed as an integral member of an existing component of a turbocharged internal combustion engine, to thereby enable use of an EGR system within the spatial confines of a modern engine compartment. It is also desirable that the component of a turbocharged internal combustion engine be adapted to incorporate at least one device of an EGR system therein both without sacrificing performance of the engine component itself, and in a manner that provides enhanced EGR system operation.